Notice how we're using RGBA colours here. This allows us to apply alpha opacity to the colour. In this case, we're giving white a 50% opacity.

Make it clickable

We know it's a button and that it can be clicked but users might not. Change the cursor to a pointer so users know they can click it.

cursor:pointer;

Hover state

We now have a pretty sexy looking button. But what about a hover state?
To save us from thinking about a colour for the hover state, we can use the RGBA approach. Let's revisit the background style. Add this after your background declaration.

background-color:rgba(255,204,0,1);

Nothing changes. All we did was change it to the same colour but using RGBA.
But how for the button's hover state, give it the same background colour but alter the opacity slightly.

button:hover{background-color:rgba(255,204,0,0.8);}

This gives us a slightly different shade of background on hover, giving the user some feedback so they know they've hovered over a clickable button.